ALL items are available from Survival reward caches and Field Upgrade (PvE level up caches).
Or...
NinjaBike Messenger bag - DZ named elite drop.
Bliss' Holster - Col Bliss (the helicopter) on General Assembly (hard).
MC Skulls gloves - any free roaming PvE boss.
Barretts Bullet Proof Vest - Boss drop (Larae Barrett) - Lexington Event Centre (Challenging).
The kneepad things - the boss in Madison Field Hospital (hard).
Ferro's mask - Joe Ferro in Napalm Production plant (hard).
So, four are available from farming hard/challenging mission. One is from the DZ, and one can be obtained from any free roaming PvE boss.
Hope this helps!